Architects, engineers, contractors, land owners and legislative initiatives have demanded increasingly sophisticated and efficient erosion control, turf reinforcement and earth reinforcement products. The term "erosion control" is used broadly in this document to refer generally and broadly to processes for restraining the movement of soil or other components of particulate substrates, whether by wind, water or otherwise, while "turf reinforcement" refers generally and broadly to processes for enhancing vegetation and turf cover on particulate substrates. "Earth reinforcement" refers generally and broadly to increasing tensile and/or shear strength of earth or particulate structures, such as in retaining wall structures, steep grades, and other applications that compel tensile and/or shear strength enhancement of particulate substrate properties. These terms are employed in broad and overlapping fashion in the field, and they are intended to be so understood in this document.
Beginning in the late 1960s in the United States, manufacturers responded to the demands mentioned above by developing rolled erosion control products. Such products, many of which originated in the Netherlands and other parts of Europe, included erosion control nets, geotextiles, erosion control blankets, geosynthetic mattings and other materials formed from natural materials such as straw and jute, as well as from synthetic materials such as polypropylene, polyvinylchloride and nylon.
Broadly speaking, such rolled erosion control products have been classified generally (and frequently imprecisely) into several categories; the industry often employs these categories interchangeably or at least partially coextensively.
First, erosion control nets classically employ two-dimensional woven natural or geosynthetic fibers or extruded plastic meshes to anchor loose-fiber mulches such as straw or hay. Such erosion control nets provide increased performance relative to hydraulically applied mulches and are suitable for moderate site conditions where open weave erosion control geotextiles and erosion control blankets are not indicated.
Second, open weave erosion control geotextiles conventionally include two-dimensional matrices of natural or synthetic yarns or ends. These products provide erosion control with or without the use of mulch and they conventionally display higher tensile strength than erosion control netting. Such products are indicated where higher tensile strength is required, such as on steeper slopes or reinforcing underlying substrate.
Third, erosion control blankets are conventionally formed of various organic or synthetic fibers which may be woven, glued or otherwise structurally connected to nettings or meshes. Common erosion control blankets include three dimensional fibrous matrices of straw, wood, coconut, nylon, polyester, polyethylene, polyvinylidine, polypropylene or other materials which are stitched, glued or otherwise fastened to nets such as erosion control nets. Blankets thus add a third dimension and are indicated at sites which require greater tensile strength and durability. Conventional applications include steep slopes (up to 40.degree.), low to moderate flow channel, and low impact shore linings. Such blankets are conventionally used only where natural, unreinforced vegetation alone is intended ultimately to provide long term soil stabilization and erosion control.
Fourth, geosynthetic mats comprise various synthetic fibers and/or filaments processed into permanent, high strength, three-dimensional matrices. Common products include cuspated polyethylene meshes that are heat bonded together, extruded monofilaments of nylon or PVC heat bonded at intersections, and crimped polyolefin fibers and other materials which are mechanically stitched between high strength nettings. Geosynthetic mats are conventionally designed for permanent and critical hydraulic applications such as drainage channels, where flow velocity and shear stresses exceed the limits of mature, natural vegetation (3 to 20 feet per second). The three dimensional profile and high tensile characteristics of geosynthetic mats entangle plant roots and soils to form a continuous composite. The combination reduces plant dislodgment during high velocity, high shear flows. Accordingly, geosynthetic mats reinforcing vegetation have recently replaced rock, riprap and other nonvegetated lining materials.
Geosynthetic mats may also be employed for turf reinforcement. In such instances, they may be overseeded or underseeded with a prescribed seed mix and/or soil to form the turf-reinforcement mat or the permanent erosion control revegetation mat.
Recently, the Erosion Control Technology Council, which is an organization formed by rolled erosion control products providers, initiated more formal classification for these sorts of products. The categories include low velocity degradable rolled erosion control products ("LVDRECP's"), high velocity degradable RECP's ("HVDRECP's"), and long term nondegradable RECP's ("LTNDRECP's"). LVDRECP's include erosion control nets, single net erosion control geotextiles, and certain erosion control blankets as discussed above. Such products are intended for a service life of one to two growing seasons and resist damage and reduce erosion only to a limited degree. They are typically indicated for slopes that feature moderate grade, length and runoff and low velocity channels where potential for damage during installation and use is minimal.
HVDRECP's include erosion control blankets with double or high strength nets, erosion control nets or erosion control geotextiles with greater strength characteristics. These products feature a service life of approximately one to five years and are indicated for steeper slope protection and higher velocity channel lining applications where natural, unreinforced vegetation is expected to provide permanent soil stabilization.
LTNDRECP's are intended to provide permanent vegetation reinforcement. These products are conventionally and usually nondegradable, high tensile strength geosynthetic mattings.
At another level, earth reinforcement materials have been used to reinforce particulate substrates. These include retaining wall structures such as reinforcement bar or geogrids embedded in soil and/or rock structures. Heavy duty and lighter duty woven natural and synthetic fiber products have also been used for earth reinforcement applications.
Conventionally, choices were forced as a particular application's set of requirements corresponded more closely to an earth reinforcement, turf reinforcement, erosion control or other application, or as those requirements changed or were expected to change over the life span of the site (e.g., erosion control may be important now, turf reinforcement later as a site matures). Erosion control conventionally required rock, riprap, or vegetation reinforced with heavy duty geosynthetic mattings. Lower flow velocities and shallower slopes made such erosion control products uneconomical, and required instead lighter duty geosynthetic mattings, erosion control blankets or perhaps two dimensional open weave geotextiles. Earth reinforcement, by contrast, required grid, heavy duty woven or other high tensile strength structures. The need has accordingly existed for a low cost, versatile product which functions effectively across a broad range of erosion control, turf reinforcement and earth reinforcement applications. Such materials would need to feature the durability approaching rock, riprap or vegetation reinforced geosynthetic mats, while featuring the low cost of lighter duty turf reinforcement materials yet the high tensile strength of earth reinforcement materials.